Stressed ribbon bridge
Encyclopedia
A stressed ribbon bridge
Bridge
A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle...

(also stress-ribbon bridge) is a tension structure (similar in many ways to a simple suspension bridge
Simple suspension bridge
A simple suspension bridge is an early type of bridge that is supported entirely from anchors at either end, and has no towers or piers. However, it may have saddles...

). The suspension cables are embedded in the deck
Deck (bridge)
A bridge deck or road bed is the roadway, or the pedestrian walkway, surface of a bridge. It is not to be confused with any deck of a ship.The deck may be of concrete,wood which in turn may be covered with asphalt concrete or other pavement...

which follows a catenary arc
Catenary
In physics and geometry, the catenary is the curve that an idealised hanging chain or cable assumes when supported at its ends and acted on only by its own weight. The curve is the graph of the hyperbolic cosine function, and has a U-like shape, superficially similar in appearance to a parabola...

between supports. Unlike the simple span the ribbon is stressed in compression, which adds to the stiffness of the structure (simple suspension spans tend to sway and bounce). The supports in turn support upward thrusting arcs that allow the grade to be changed between spans (where multiple spans are used). Such bridges are typically made from concrete reinforced by steel tensioning cables. Where such bridges carry vehicle traffic a certain degree of stiffness is required to prevent excessive flexure of the structure, obtained by stressing the concrete
Prestressed concrete
Prestressed concrete is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete...

in compression.

## Two examples

The Maldonado bridge, located in Maldonado, Uruguay
Maldonado is the capital of Maldonado Department of Uruguay. It is located on Route 39 and shares borders with Punta del Este to the south, Pinares - Las Delicias to the south and to the east and suburb La Sonrisa to the north. Together they all for a unified metropolitan area. East of the city...

, illustrated below, was created by the engineer Leonel Viera (1913-1975) to expand the area of Punta del Este
Punta del Este
Punta del Este is a resort town on the Atlantic Coast in the Maldonado Department of southeastern Uruguay. It is located on the intersection of Route 10 with Route 39, directly southeast of the department capital Maldonado and about east of Montevideo...

. This pioneered the construction sequence now typical for concrete segment bridges of this type. After placement of the principal cables, precast concrete tiles were placed to form the initial structure. The cables were then prestressed
Prestressed concrete
Prestressed concrete is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete...

by loading sandbags upon the tiles, followed by final concretization of the gaps between tiles. Removal of the sandbags then compressively stressed the concrete structure, enhancing its stiffness and durability under load. An identical bridge was later constructed parallel to the first.

The concrete segment stressed ribbon footbridge
Footbridge
A footbridge or pedestrian bridge is a bridge designed for pedestrians and in some cases cyclists, animal traffic and horse riders, rather than vehicular traffic. Footbridges complement the landscape and can be used decoratively to visually link two distinct areas or to signal a transaction...

shown below carries pedestrians, bicyclists, and pipelines across the Rogue River
Rogue River (Oregon)
The Rogue River in southwestern Oregon in the United States flows about in a generally westward direction from the Cascade Range to the Pacific Ocean. Known for its salmon runs, whitewater rafting, and rugged scenery, it was one of the original eight rivers named in the Wild and Scenic Rivers Act...

at Grants Pass, Oregon
Grants Pass, Oregon
-Rogue River:The Rogue River runs through Grants Pass.-Demographics:As of the census of 2000, there were 23,003 people, 9,376 households, and 5,925 families residing in the city. The population density was . There were 9,885 housing units at an average density of 1,303.3 per square mile . By 2008,...

.